Optical zoom and image-rotating system

ABSTRACT

Optical systems for microfilm readers or the like having image rotation capabilities and zoom lens means for selectively varying the image magnification. The optical systems include an aperture stop positioned remote from the microfilm and substantially adjacent the projection screen for maintaining constant screen brightness through a broad range of magnification.

5a m 3,582 12m Arthur Cox Park Ridge. Ill. 750,6]2

Aug. 6, 1968 June I, 1971 Bell & Howell Company Chicago, Ill.

Inventor Appl. No. Filed Patented Assignee OPTICAL ZOOM'AND IMAGE-ROTATING SYSTEM 3 Claims, 13 Drawing Figs.

U.S. Cl 353/25, 350/184, 350/203, 350/215, 353/81, 355/56 Int. Cl. ..G03b 21/28 Field of Search 353/81, 74-78, 95, 96,102, 25-27; 355/18, 53, 56,57,

8... it M113 [56] References Cited UNITED STATES PATENTS 2,434,378 l/l948 Wekeman 355/66X 2,815,696 l2/1957 Brownscombe. 353/76X 3,286,592 11/1966 Wagner et al.... 350/203X 3,354,776 1 1/1967 Smitzer 353/76 3,497,289 2/1970 Oberheuser 350/203X Primary Examiner-Robert B. Hull Assistant Examiner-Steven L. Stephan Attorneys-Jack H. Hall and Gerald M. Newman ABSTRACT: Optical systems for microfilm readers or the like having image rotation capabilities and zoom lens means for selectively varying the image magnification. The optical systems include an aperture stop positioned remote from the microfilm and substantially adjacent the projection screen for maintaining constant screen brightness through a broad range of magnification.

. PATENTEU JUN IIEIII SHEET 1 or 5 PATENTED JUN 1 I97! SHEET 2 BF 5 Incierzllbr \flrihur Cox.

PATENTEU JUN 1 197i SHEET 3 BF 5 OPTICAL ZOOM AND IMAGE-ROTATING SYSTEM This invention relates to optical systems for projection-type microfilm readers.

The principal object of the invention is to provide an improved cabinet-projector-type microfilm reader having prism means for projecting the image of each frame in an upright position even though two frames on the microfilm are differently oriented, and having zoom lens means for varying the magnification attwill through a 1.3-to-l range or more.

Further objects will be pointed out with reference to the aceompanying drawings, in which:

FIG. 1 is a schematic or block diagram of an optical system according to the invention.

FIG. 2 is a diagrammatic cross section of a zoom lens according to the invention.

FIG. 3 is a diagrammatic cross section of a prime lens according to the invention, particularly designed with its aperture stop in front of the lens for use with a zoom projector.

FIG. 4 is a diagrammatic cross section of a combined'image rotator and angle spreader according to the invention, which is useful with any projector within its limits of aperture and field angle.

FIG. 4A is an elevational view of the image rotator shown in FIG. 4, as viewed from the right end thereof.

FIG. 5 is a diagrammatic cross section of a zoom condenser system according to the invention and of the sealed reflector lamp with which it was particularly designed to be used.

FIGS. 6 and 7 show a mechanism for varying the condenser for maintaining optimum illumination.

FIGS. 8 to 11 show an adjustable mount for the angle spreader lenses and the prism enclosed therebetween.

FIG. 12 shows another form of zoom lens with which the angle spreader is adapted to be used.

It is a further object of the invention to provide an optical system for a microfilm projector as outlined in FIG. 1 consisting of a lamp 10, a zoom condenser system 11, a film gate 12, a prime lens 13 for projecting an image of film l2 placed in the film gate, a zoom lens 14 for varying the magnification at the option of the user, a combined image rotator and angle spreader 15, a system of mirrors 16, 17, 18 (shown in much reduced scale) for folding the path of the projected beam, a fine grain projection screen 19 and means for automatically adjusting the condenser for optimum illumination when the zoom lens is adjusted for changing magnification.

A further object of the invention is to provide an improved zoom lens, as shown in FIG. 2, characterized in part by having its aperture stop outside the zoom lens toward the long conjugate end of the system whereby the brightness of the projected image remains constant, provided the incident light fills the aperture.

A further object of the invention is to provide an improved prime lens as shown in FIG. 3, having general utility in projectors requiring the aperture stop to be at a distance in front of the body of the lens, and which is particularly useful in combination with the zoom lens of FIG. 2.

A further object of the invention is to provide a combined angle spreader or wide-angle attachment and image-rotating prism, as shown in FIG. 4, whereby image rotation can be accomplished throughout a wider angular field than the intrinsic angular limits of the prism.

An object of a particular feature of the invention is to provide an image rotation prism having the aperture stop for the system near the optical center of the prism.

An object of a further feature of the invention is to provide a rotatable mount for the angle spreader and prism, as shown in FIGS. 8, 9, l and 11 which is inexpensive to manufacture and easy to adjust for proper alignment of the prism and lens elements with each other and with the axis of rotation.

FIG. 1 is a block diagram of an illumination and optical system for a microfilm reader or the like, according to the invention. An incandescent lamp l0 and condenser 11 (see FIG.

) illuminate a film gate 12 of known construction. For clarity of description the microfilm copy 12' of printed matter is placed in the film gate for projection. A projection lens or prime'lens 13 (see FIG. 3) forms either a real or a virtual image of the microfilm. A zoom lens 14 (see FIG. 2) in turn forms an image which may be varied in size at the option of the user. The zoom control is of known construction having a helical groove and a specially shaped slot, both formed in a rotatable lens tube.

Forwardly of the zoom lens is a combined angle spreader and image rotator 15 (see FIGS. 4 and 4A) which receives light rays from the zoom lens and projects an enlarged image which may be rotated by the user so that the printed matter is right side up. The rays projected from the angle spreader are reflected in three plane mirrors l6, l7 and 18 which fold the optical path for compactness. The image is finally formed on a projection screen 19 for viewing from the front.

Mirror 18 is mounted on a hinge and may be pivoted to position 18' thereby allowing the image to be formed on a platen 20 normally supplied with photosensitive paper for making a photocopy reproduction of the printed matter.

The optical system has been designed to correct for spherical aberration, coma, astigmatism, distortion, lateral color, and combined variations of these aberrations, over the whole of the projection screen for all positions of the zoom control. The combination of angle spreader and pechan prism is par ticularly favorable to the establishment of such an aberrational correction.

Each known prism type has its characteristic limiting angle of field, and outside this angle no useful light (or too little light) passes through. By combining the pechan prism with an angle spreader, a wider angular field is projected than could otherwise be projected through this type of prism. The dove prism may have a wider limiting angle of field but must be used with substantially collimated light. The present invention combines the wider field angle with the additional advantages derived from the entry and exit faces of the prism being perpendicular to the optical axis.

FIG. 2 shows a zoom lens according to the invention adapted to operate with an aperture stop 21 forwardly thereof. When assembled as part of the complete system, a stop is provided either adjacent to or within the image rotator. (FIG. 4). The zoom lens consists of a front stationary member L, to L,, a zooming member L to L of negative power and a compensation member L, to L all mounted in known manner for moving the zooming member in one direction for changing the magnification and moving the compensation member first one direction and then in the other direction for maintaining the image position. The ,radii of curvature R to R the thicknesses t to t of the lens elements, the spacing between certain lens elements s, to 5, the refractive indices n for the D line of the spectrum and the Abbe dispersion numbers V are as listed in table I. The and signs indicate curvature convex and concave to the front, respectively. Dimensions are in inches but of course may be scaled to a larger or smaller size.

Table l-(onlinued TABLE III 85 07 5 R=-.ssa l Ri=+2 765 L, t;=.070 n=l.607 \'=55.6 Ln. l|=.l80 n=1.717 V=m5 Y Rn=+61303 i Rz=8.333 L9 r=.ll n=1.805 V=25.5 L2 iz=.080 n=1.575 V=4l.3

-1.509 I l R;=+1.429

a1=( 8i=.os5 R17=7.077 l R4=+2.5UO L1, tl =.200 n=l.517 V=64.2 L; t;=.080 7L=L575 V=41.3

Ru=-Q.OOS R5=+L420 a5=.005 s =.210 Rn=l'20.00 I l0 L m=.200 n=l.620 V=60.3 Pi and PL. t,,=4.621 n=1.697 V=55.6

a=.005 s;=.100 R3I=+5.750 Rs=4.545 L11 tn= 275 n=l.620 V=60.3 L4 f4=.065 n=1.648 V=33.9

R2z=2.538 R7=23.53O

m=.0os s t5=.100 n=1.572 v=51.5 R 4.439 15 a= L1; ti3=.090 n=l.805 V=25.5

1.68IW.A,448M,.035TP 2-0621W-A 518 M4 T P FIGS. 8, 9, 10 and 11 are views of the novel mount for the image rotator and angle spreader. A pullylike ring 81 is FIG. 3 shows the prime lens and table II gives the lens data in the same manner as table I. The flat plate L, forms a part of the film gate.

TABLE II Ri=+3.333 L ti=.275 n=l.620 V=60.3

8i=.0065 R =3.509 L7 tg=.100 7I=1.805 V=25.5

8z=.005 R5=+L724 L t =.220 n=1.620 V=60.3

83=1i550 R =+1A93 L4 t4=.200 n=1.518 V=59.0

84:.115 Ro=1.818 L5 l5=.100 1L=1.805 V==25.5

is=.200 n=1.526 V=5LO Rn=+2.966

\J FIG. 4 shows the combined an le s reader and ima e rotaoi' in axial section and FIG. 4A shows the prisms P and P in elevation. The image rotating prism and its principle of operation are well known and are fully described in various well- "I known optics books. An odd number of reflections are m required (five in this case) and the axial ray emerges along the identical straight line along which it entered. Two reflections take place by total internal reflection at a pair of closely spaced internal surfaces which are traversed by the beam between these two reflections. It is believed to be be novel to insert a thin sheet of opaque material between these surfaces as indicated by a section line in FIG. 4. The sheet of opaque material is provided with an opening (normally round) which functions as the aperture stop of the system. It should be noted that an aperture stop in this position (about midway between the two members) is favorable for uniform illumination of the projected image while retaining a prism of compact physical size.

Alternatively, using a similar pechan prism, the sheet of opaque material may be eliminated and the internal diagonal surfaces aluminized except for an aperture stop formed by a circularly shaped, nonaluminized, clear area through which the reflected rays may pass without restriction.

The angle spreader includes fine lens elements I. to 1. and is especially designed for correction of the image aberrations in conjunction with the prism between the two members. Constructional data for this lens is given in table III in the same manner as above.

rotatably gripped by a mating bearing (not shown) on the cabinet. The bearing, of course, is made in at least two pieces for inserting the pulley. The body 82 of the prism mount may be formed integral with the pulley and consists of two rings 83 and 84 rigidly connected by a horizontal bar 85. The bar 85 is flat on the face toward the axis of rotation for receiving a lower plate 86 ofa prism clamp assembly, which in turn is held to an upper plate 87 by screws 88 for clamping the prism. The prism unit is held against bar 85 by a tongue and pin 89 inserted in the front ring 84. This pin has sufficient play for rotatably adjusting the prism about pin 90 by engaging a hole in bar 85 until it is finally firmly held by screws 91.

A front lens mount 93 is held against thefront ring 84 by three screws 95 which pass through oversized holes in the lens mount. Before these screws are tightened, the mount is adjusted by rotation about pin 94 engaging a hole (not shown) in ring 84 so that the axis of the lenses L to L is adjustable in a substantially vertical direction along the central portion of a circular are 96.

The rear lens mount 103 is mounted against the rear ring 83 for adjustment of its axis in a horizontal direction along are 106 by slight rotation around pin 104 in exactly the same manner before screws 105 are finally tightened.

Directions for alignment during manufacture are as follows:

1. Line up a collimator and an autocollimator and then insert the image rotator with lens 1-5 of FIG. 4 temporarily removed.

2. Mount a plane parallel mirror on the rear face of the pulley 81 and adjust the entire unit so that this mirror is perpendicular to the autocollimator axis.

3. Remove the plane mirror and adjust the pechan prism about pivot 90 so that the collimator image lies as close as possible to its original position in the autocollimator and tighten screws 21.

4. Insert lens 1-5 of FIG. 4, adjust the front and rear cells about pins 94 and 104 so that all coma is removed from one collimator image and tighten screws 95 and 105.

5. Screws 91, 95 and 105 may be fixed with cement to prevent later disassembly by the customer who may not be equipped to realign the parts.

FIG. 5 is an optical diagram of the condenser system including a ISO-watt projection lamp 10 with sealed-in reflector. Mirrors M and M allow the condenser system to be folded into a small cabinet. One member, consisting of two lenses L and L is movable for maintaining optimum illumination during zooming. The mechanism for moving these lenses is described below with reference to FIGS. 6 and 7.

The constructional data for the condenser system is given in table IV. The radii are convex to the front, but because of the folding of the system the front is sometimes to the left and sometimes to the right. The consistent rule is that the light from the lamp enters each lens from the rear and leaves it through the front surface.

6 TABLE IV Table V-Continued R l Lo t=.100 n=1.805 v=25.5 L1, v. ir l n=.100 n=1.611 v=5s.s zt g m 1= 5 L 7 l1o=.310 1z=1.640 V=60.2 i R1 -l0.000

.rz=l.975 87=.005 R: m 11=L523 V=58fi L RIPH'M l1 .400 n=1.640 V=60.2

R|=3.000 R1o=+50.000 R =+3 000 3:950 Lu R 1493 m=.1oo n==1.805 v=25.5 L1 5 zt=aoo L t1 =.340 n=1.640 v=60.2

R6 Rz +9.52! M (45 8|==1J25 R +900 0 8a=.0235

$1.325 L ,,=,1a0 F1305 v=25.5 R7=+4.540 R,,=+4.s5s L4 h==.240 fl=1.523 V=58.6 BF= 743 Raw to 2.007 Rn=3.080 L, s 100 n=1.523 V=58.6

Riu=+3.080

8;=.082 L6 R" 3'080 5:400 z v= g 20 It is obvious that upon study by those skilled in the art the 8 047 to 247 disclosed invention may be altered or modified both in physi- R w h cal appearance and construction without departing from its in- L1 R 250 1:225 7:535 ventive concept. Therefore, the scope of protection to be given this invention should not be limited by the embodiments L8 n RIF-F2350 tFfio n=mu v=58 8 described above, but should be determined by the essential RN=9J00 descriptions thereof which appear in the appended claims. Q=+ R030 The embodiments of the invention in which I claim an ex- Lw !n=-3 0 V=533 clusive property or privilege are defined as follows:

RIP 1. An optical system for a cabinet-type microfilm projector comprising the following parts operatively aligned on an optical axis: (1) a light source and mirror unit; (2),a condenser; (3) a film gate through which the condenser is adapted to 5 and 7 Show the mechanism for moving the direct light from the lamp; (4) a prime lens for projecting an denser lens elements L L under the control of the zoom lens image f fil l d i h fil t (5) a o m len h vi g a 14. The sleeve 61 of the zoom lens is turned for zooming in the bl Zooming member f varying he ma ifi ti n manner know" mechanical compensation y through a range of at least 1.33 to l at the option of the user; This SIeCVC iS provided a toothed ring engages a a combined angle preader and image rotation unit con- Pinion mmmted with a friction P y 64 on an auxiliary sisting of a positive lens component adjacent the zoom lens, a A flexible cable 66 is wrapped around the P y 64 a negative lens component spaced therefrom and a pechan-type sufficiemynumbel' of times (about 3) P pp g and 40 inverting prism therebetween having two closely spaced interis p under tension y coil p g This cable Passes nal faces through which the light beam passes, the whole unit over an idler pulley 70 and is attached to a sliding carriage 71 being mounted f i-otation around h i l i (7) a whlch are mounted the lens elements 5 and a for move system of three mirrors for folding the projected beam of rays ment according to the invention. The angular movement of f r i id image d (8) a fi grain diffu ing Screen upon the sleeve 61, the gear ratio of the ring 62 to the pinion 63 and hi h the projected image may be viewed, characterized by the diameter of the friction P y 64 6 designed in a Well having the aperture stop for the projection system between the known manner to produce a movement of about 1.8 inches. cioseiy spaced fa e of h pechan prism and by a lens 12 shows another Zoom lens and Prime lens syslem ponent of the condenser being movable under the control of With which the angle spreader and image rotator iS adapted to the movement of the ooming member of the oom lens be used. The constructional data for this system are given in h b optimum ill i i i i i d throughout h Table V and it should be noted that l.805/25.5 glass, which is Zooming range, available with the usual yellow color almost removed, should An optical System as claimed in claim 1 further charac be uuhzed' terized by having one of the three mirrors mounted for optional movement to a position outside the projected beam whereby the image is projected to an alternative image posi- TABLE V tion and by having means for supporting photosensitized paper in said alternative image position. Ll R'=+1'196 1:220 7:60; 3. An optical system comprising the following parts opera- R:=6.757 tively aligned on an optical axis: (1) a light source; (2) a con- Ra: +2033) T080 "=LB05 denser; (3) a film gate through which the condenser is adapted 8:=.4695; .2550 to direct light from said source; (4) a prime lens for projecting La ,FDSO 11:1.697 an image of film placed in the film gate; (5) a zoom lens hav- R5=+L610 ing a movable zooming member for varying the magnification RFmgs Edam 65 of said image; (6) a combined angle spreader and image rota- L4 h t4=.080 n=l.697 V=65.6 tion unit consisting of a positive lens component adjacent to L5 3:230 71=L8O5 the zoom lens, a negative lens component spaced therefrom Ri=-16.13 and a pechan-type inverting prism, the whole unit being 51 "Flow; 3185 mounted for rotation around the optical axis; and (7) a screen e t=.250 n=1.640 V=60.2 disposed in the light path upon which the projected image may a: 005 be viewed wherein said optical system is characterized by an Rn=14.29 aperture stop between the closely spaced faces of the pechan L7 7:602 prism and movement of a lens component of the condenser e5=.060 responsive to movement of the zooming member of the zoom La Rl3=+4m ,FAOO F1540 7:602 75 lens whereby constant illumination is maintained throughout Ru= 2.857 the zooming range. 

1. An optical system for a cabinet-type microfilm projector comprising the following parts operatively aligned on an optical axis: (1) a light source and mirror unit; (2) a condenser; (3) a film gate through which the condenser is adapted to direct light from the lamp; (4) a prime lens for projecting an image of film placed in the film gate; (5) a zoom lens having a movable zooming member for varying the magnification through a range of at least 1.33 to 1 at the option of the user; (6) a combined angle spreader and image rotation unit consisting of a positive lens component adjacent the zoom lens, a negative lens component spaced therefrom and a pechan-type inverting prism therebetween having two closely spaced internal faces through which the light beam passes, the whole unit being mounted for rotation around the optical axis; (7) a system of three mirrors for folding the projected beam of rays forming said image and (8) a fine grain diffusing screen upon which the projected image may be viewed, characterized by having the aperture stop for the projection system between the closely spaced faces of the pechan prism and by a lens component of the condenser being movable under the control of the movement of the zooming member of the zoom lens whereby optimum illumination is maintained throughout the zooming range.
 2. An optical system as claimed in claim 1, further characterized by having one of the three mirrors mounted for optional movement to a position outside the projected beam whereby the image is projected to an alternative image position and by having means for supporting photosensitized paper in said alternative image position.
 3. An optical system comprising the following parts operatively aligned on an optical axis: (1) a light source; (2) a condenser; (3) a film gate through which the condenser is adapted to direct light from said source; (4) a prime lens for projecting an image of film placed in the film gate; (5) a zoom lens having a movable zooming member for varying the magnification of said image; (6) a combined angle spreader and image rotation unit consisting of a positive lens component adjacent to the zoom lens, a negative lens component spaced therefrom and a pechan-type inverting prism, the whole unit being mounted for rotation around the optical axis; and (7) a screen disposed in the light path upon which the projected image may be viewed wherein said optical system is characterized by an aperture stop between the closely spaced faces of the pechan prism and movement of a lens component of the condenser responsive to movement of the zooming member of the zoom lens whereby constant illumination is maintained throughout the zooming range. 